The Heart

• The circulatory system is an organ system that transports oxygen and nutrients to our body's tissues.
• The circulatory system relies on three main things: the blood which carries the oxygen and nutrients, the blood vessels which hold that blood, and the heart which pumps the blood to keep it moving through the vessels.
• The circulatory system can be conceptualized as a double circulatory system with two distinct loops: one carrying deoxygenated blood from the heart to the lungs where it gains oxygen and then flows back to the heart, and the other carrying the oxygenated blood to the rest of the body where it gives up its oxygen to the tissues and then flows back to the heart.
• The heart consists of one, two, three, four chambers with thick muscular walls surrounding them and veins and arteries coming in and out.
• The top chambers of the heart are called atria with an individual one being called an atrium, and the bottom chambers are ventricles.
• Between the chambers and the vessels of the heart, we find valves which prevent the blood from flowing backwards ensuring that it always flows in the right direction.
• The path the blood takes as it passes through the heart is: it flows into the heart via the vena cava and the pulmonary vein, then into the right atrium and left atrium respectively, then into the ventricles, and finally out into the pulmonary artery and the aorta.
• The heart has a group of cells in the right atrium that act as a pacemaker and these pacemaker cells produce small electrical impulses which spread through the muscular walls of the heart causing them to contract.
• In some rare cases, these pacemaker cells don't work properly, and to fix this, doctors can implant an artificial pacemaker which is a small device that we place just under the skin above the heart and as a wire that can carry electrical current down to the heart, telling it to contract regularly.
• The term artery refers to any vessel that carries blood away from the heart, while a vein is any vessel that carries blood to the heart.
• The heart also needs its own supply of oxygenated blood and it gets this through small arteries that branch off the aorta called coronary arteries.
• These vessels encircle the heart to make sure that the muscle tissue gets all of the oxygen and nutrients that it needs.